It seems that you are making more work for yourself than you rightly need to. It is for just this type of scenario that I wrote the CGI::Upload module - This module allows you to check file upload type by both contents (using File::MMagic and MIME magic numbers ) and file extension.

For example, using the CGI::Upload module, this code could be reduced to the following (comments included for explanation) :

use CGI;
use CGI::Upload;

my $cgi = CGI->new;
my $upload = CGI::Upload->new;

#   The array @types contains a list of allowed file
#   extensions - Note that testing a file by MIME type is 
#   more secure than depending upon the file extension 
#   alone.

my @types = qw/ gif jpg jpeg jpe jfif /;

#   Loop through each of the image upload fields.  The 
#   image field names are being used here in place of the 
#   loop index - This has been written thus so that 
#   additional image upload fields, which may not 
#   necessarily be named 'im<num>' can be added.

foreach ( qw/ im1 im2 im3 im4 im5 / ) {

    #   Ensure that the CGI parameter has been defined

    if ( $cgi->param($_) ) {

        #   Check the file type of the uploaded file with the list
        #   of allowed file types in @types (grep works nicely
        #   for this) - If the image file extension is not within
        #   the array @types then return an error to the user.

        unless ( grep /\Q$upload->file_type($_)\E/ @types ) {

            error('Your image needs to be in GIF or JPEG format');

        }
    }
}
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perl -e 'print+unpack("N",pack("B32","00000000000000000000000111001011")),"\n"'